1. Field of the Invention
The present invention relates to a toner conveying member, a developing device including the toner conveying member, and an image forming apparatus including the developing device.
2. Description of the Related Art
An electrophotographic image forming apparatus is equipped with a developing device in a two-component developing system using a developer containing toner and a carrier or in a one-component developing system using only toner without using a carrier. Such a developing device is provided with a developing roller, and is also provided with a toner conveying member for conveying toner and stirring and mixing toner and a carrier. The toner conveying member is a member with a conveying blade (screw) having a spiral shape or the like arranged on a shaft.
The image forming apparatus is also equipped with a toner supply device for supplying toner from a toner container to the developing device. A toner conveying member may also be used in the toner supply device. Some image forming apparatuses are equipped with cartridges into which a developing roller as a developer carrier, a toner supply device (a toner storage unit, a toner conveying member, a toner supply roller, etc.), and so on are integrated. Of them, a cartridge including a photosensitive drum as an image carrier is also called a process cartridge.
JP 2011-22467 A discloses a developing device (development container) including a toner conveying member. As shown in an axial cross section thereof in FIG. 1, the toner conveying member (mixing and stirring member) 200 has a conveying blade 202 made of resin and a rotating shaft (rotating shaft) 201 made of metal. With this, the developing device prevents the longitudinal deflection of the toner conveying member 200 due to rotation, and continually keeps the distance between the toner conveying member 200 and a detecting surface of a toner concentration detection sensor attached to an inner wall in the development container constant, thereby to stabilize the output of the toner concentration sensor.
JP 2014-115402 A discloses a toner conveying member with a shaft made of resin and a conveying blade made of metal. JP 2014-115402 A also discloses a toner conveying member with a shaft made of metal and a conveying blade made of resin or metal.
However, with the technique described in JP 2011-22467 A, the longitudinal deflection of the toner conveying member due to rotation can be prevented, but the distance between the toner conveying member and the detecting surface of the toner concentration detection sensor is made excessively constant. Therefore, although this technique stabilizes the output of the toner concentration sensor, it causes a problem that a developer conveyed over the detecting surface adheres to the detecting surface such as when the electrical charge of toner increases too much, and thus the correct output of the toner concentration sensor cannot be obtained. Further, with this technique, a metal shaft is present along the entire longitudinal length, which eliminates a problem such as deformation or breakage due to drive stress but causes a problem such as a cost increase.
In the technique described in JP 2014-115402 A, the toner conveying member with the shaft made of resin and the conveying blade made of metal longitudinally bends at the shaft made of resin, causing a developer on a detecting surface to pulsate, and making it hard for the developer to adhere to the top of the detecting surface. Thus, it can solve the above-described problem.
However, a toner conveying member with a shaft made of resin as described in JP 2014-115402 A permanently deforms relatively early at the shaft of the resin material, preventing a developer from being conveyed axially smoothly. Thus, in view of the recovery and recycle of cartridges, it causes a new problem that the number of recyclability of the toner conveying member decreases.
As shown in FIGS. 2A to 2C, it is also considered to put metal pipes (metal collars) 303 on end portions of a shaft 301 (end portions at both ends of a screw 302) of a toner conveying member 300 with the shaft 301 made of resin, to reduce the above new problem. The provision of the metal pipes 303 only at portions corresponding to bearings as illustrated not only reduces the above new problem but also has an advantage of being able to use them also as bearing members. FIG. 2B is an enlarged view showing an axial cross-sectional shape of the toner conveying member in FIG. 2A, and FIG. 2C is a cross-sectional view in the direction C-C in FIG. 2B.
However, when a developer is injected into a development container and a rotation operation is executed, the toner conveying member 300 like this goes into a state where a deflection due to rotational drive occurs, that is, a state where bending occurs. Stress under this state causes a troublesome phenomenon such as rubbing against an inner wall of the development container, the wear of a drive transmission gear, or a deformation at a bearing portion and the vicinity.